1. Field of the Invention
The present invention relates to high solids polyurethane-urea dispersions, to a process for their preparation and to their use in lacquers and coating compositions.
2. Description of the Prior Art
Aqueous binders based on hydrophilically modified polyurethanes or polyurethane-polyureas are known as described, e.g., in Houben-Weyl, Methoden der organischen Chemie, Vol. E 20, p. 1659 (1987), "Advances in Urethane Science and Technology", Vol. 10, p. 121-162 (1987), Ullmann's Encyclopedia of Industrial Chemistry, Vol. A 21, p. 677 (1992).
The known aqueous dispersions generally result in coating compositions having a very good properties, which, depending upon the composition, are suitable for a very wide variety of applications. The spectrum ranges from hard, abrasion resistant coatings, which may be used for coating floors, to soft, highly elastic coatings, which are suitable for coating textiles.
Although the prior art includes a large number of various types of polyurethane dispersions, even better polyurethanes and polyurethane-polyureas are required. There is a need for the dispersions to have high molecular weights, to have solids contents of at least 40% at low viscosity, despite a high ionic group content, and to be storage even in highly diluted form.
The high contents of ionic groups are necessary to increase the stability of the dispersions or the formulated coatings compositions based on these dispersions and guarantee optimum pigment wetting, so that the resulting coatings have very good optical properties. However, in dispersions of high molecular weight polymers, high ionic group contents generally lead to very low solids contents. High molecular weights are indispensable in applications in which no or only a slight chemical crosslinking reaction takes place after application and good stability properties are nevertheless required. In some fields of application, such as in metallic basecoats or in wood varnishes, dispersions are frequently used in highly diluted form. Good stability must be ensured even in such high dilutions.
An object of the present invention is to provide polyurethane-urea dispersions which, in addition to good stability, also dry rapidly, have a minimum film-forming temperature &lt;0.degree. C. without the addition of organic solvents, and have very good cleanability (i.e., dried-on polyurethane films or polymer residues or lacquer overspray from application installations or application tools can be removed).
This object may be achieved with the polyurethane-urea dispersions according to the present invention, which are described hereinafter.